This invention relates to balancing a simulation platform in particular for aeronautical systems, and especially such a platform, a method and a balancing device.
The simulation of equipment items is a field separate from the actual operation of such equipment items, in particular because of the fact that it takes part, to a great extent prior to operation, in the development of these operating equipment items.
In a standard function, through the use of software or hardware models representative of the performances of systems and their environments, simulation makes it possible to considerably reduce development costs.
In the specific field of aeronautics, new aircraft architectures generally are developed by simulating all or part of the equipment items making up these architectures.
A simulation platform thus has various proportions of equipment items corresponding to the systems of the aircraft, in particular in the form of real equipment items and/or equipment items simulated by a software model (engine, flight control laws, fuel, hydraulics, etc.), and software models representative of components of the environment in which the aircraft is led to travel or of the pilot's cockpit (visual, aerodynamics, flight mechanics or other aspects of the environment of the aircraft such as atmosphere, ground, etc.).
All the software models and real equipment items adopted constitute the components of the simulation platform. Each component has a transfer function or “distinctive dynamic,” linking its inputs to its outputs. These components are brought together and interact with the aid of data flows circulating through inputs/outputs of a general simulation application.
Aircraft simulation generally is used to develop and validate airplane systems in the entire performance envelope, for example at take-off, in approach/landing phase or in cruising.
During actual simulations by an operator, the simulation platform and application thus are set to an initialization mode by which the simulated aircraft is positioned in space, placing it in a stable static and dynamic balance taking into account the simulated environment of the aircraft. This positioning and this balance therefore are led to vary considerably according to the flight parts to be simulated.
Once this balance is achieved, the application is changed over to operational simulation mode consisting in executing the simulation of the aircraft by reproducing the functional aspect of the aircraft from its balance position during a given flight phase.
This preliminary balancing of the aircraft is crucial in order to be able to effect a changeover to operational mode under the best conditions, in particular avoiding any discontinuity of the state of the simulated systems. Such a discontinuity in fact may well make the performance of the simulated aircraft, and therefore of the simulation platform, possibly implemented in the form of an articulated prototype, uncontrollable. Such a prototype on jacks controlled by the simulation operation and possible holding operators then may fall, causing injuries.
Balancing generally consists in determining a configuration of the controls (movable surfaces, engine thrust) and other parameters of the aircraft, according to its position in space, its velocity vector and/or acceleration (amplitude and orientation) and atmospheric conditions chosen prior to the start of the simulation.
By way of example, one may be led to calculate the airplane attitude and the positions of the elevator, rudder, aileron and throttle controls, which make it possible to attain target values for the following linear and angular accelerations {dot over (U)}x1, {dot over (U)}y1, {dot over (U)}z1, {dot over (P)}1, {dot over (Q)}1 and {dot over (R)}1 or corresponding speeds Ux1, Uy1, Uz1, P1, Q1 and R1.
This determination is not without difficulty, given that the simulation components, whether they are the real equipment items or simulating equipment items supplied by subcontractors, more often than not are “black boxes” the transfer functions of which remain unknown.
Among the various conceivable balancing methods, one may consist in reusing airplane parameter recordings made during flights for example, in order to determine the configuration of the aircraft according to the desired target values. Such a solution, however, cannot be used during the process of manufacturing a new aircraft, since the latter has not yet flown. Moreover, this method makes it possible to achieve a balancing only in a limited number of configurations because it is based on a limited number of recordings. It therefore is impossible to balance all the desired situations.
A second method consists in staging a flight of the aircraft from a fully known balance position (generally stationary before take-off) until same is in the desired position. This solution, however, is costly in time (flight time) and is highly sensitive to any modeling error of the model used for staging the flight.
A third method, more widely used, employs a simulation model within the application of the same name for balancing purposes only. This simulation model connects the variables of control U (position of the controls of the airplane, for example) to be determined to the values of output Y, of speed and acceleration type.
Balancing is carried out axis by axis (longitudinal, lateral) on the basis of a linear servoing of the simulation model, seeking to have the values of output Y converge toward the desired target values Yc: U=K (Yc−Y), up to a certain threshold defined by the user or the developer. During this phase, various simulation components are called upon, in particular the flight mechanics, the atmosphere, the flight controls or even the engines.
The simulation model generally is established without precise knowledge of the transfer function of the equipment item concerned.
The choice of the variables servoed and set according to the target flight point is made with the aid of common sense and a good empirical knowledge of balancing.
By way of example, in the case of servoing of the longitudinal speed Ux1 with thrust T, the servoing used by this third method appears in the form: T=K·(Ux1c−Ux1).
This third method, however, also has certain drawbacks. In particular, the method is sensitive to errors due to modeling of nonlinear systems as simple linear models.
That means on the one hand that the rougher the modeling, the more erroneous the control variables supplied. On the other hand, precise models are very bulky, so that a simplification of the modeling is widely sought in order to reduce processing times.
That also means that the method does not offer any generic quality for simulation from one flight point to another or from one aircraft to another. A new model then must be used and/or new parametrizations must be carried out in order to take into account this change of flight point or aircraft resulting from a leveling between two simulations.
Furthermore, the simulation time necessary for achieving the sought balance is not deterministic in this method. It therefore generally is necessary to limit the balancing time and to use the resulting, approximate, corresponding control variables.
Finally, this method is not repetitive because of numerical shifts introduced by the linear servoing. Different states of the aircraft thus are obtained for the same positioning thereof. Yet this property may prove to be significant when the effect of a parameter on the performance of the aircraft is analyzed by reproducing the simulation several times from the assumed same balance point.